Method for the removal of unwanted portions of an article by spraying with high velocity dry ice particles

ABSTRACT

A method for the removal of unwanted portions of an article such as membranes, burrs and flashing utilizing solid particles of dry ice (carbon dioxide at a temperature colder than about -56 DEG C) which are impacted against the unwanted portions is described. Kinetic energy imparted to the dry ice particles causes removal of the unwanted portions of the article upon impact. In addition, the dry ice particles cool the impacted area and with thermoplastic and elastic materials thereby embrittles thin sections of flashing and burrs and the like making them more easily removable by the impact of the dry ice particles.

United States Patent Rice et al. 1 Nov. 14, 1972 [54] METHOD FOR THE REMOVAL OF 2,881,571 4/1959 Granata ..5l/3l4 X UNWANTED PORTIONS OF AN 2,996,846 8/ 1961 Leliaert ..51/ l3 ARTI LE BY SPR YIN WI H 3,110,983 11/1963 Moore ..51/314 X VELOCITY DRY ICE PARTICLES 3,137,101 6/1964 beliaert ..S1/ 13 3,160,993 12/1964 McCormick ..51/13 X [721 lnvemrs= g P gs; m 3,324,605 6/1967 Lester 1/314 ankhn! o n I, C

[73] Assignee: Chemolronics International, Inc., Prim? Examiner-Donald Kelly Ann Arbor, Nlich Attomeylan C. McLeod et al.

[22] Filed: July 12, 1971 57 ABSTRACT PP 161,907 A method for the removal of unwanted portions of an article such as membranes, burrs and flashing utilizing l. 1 31 1 320, s 2 Particles dry ice (calm dixide a tempera {ii} iii 8 .f.f...f.f.f...m4ifioi we colder than about which are impacted [58] Field of Search ..51/320, 8, 13, 164.5, 314, again a g g i li Kinetic energy imparte to e ry 1C6 parttc es causes 51/315 83/22 177 removal of the unwanted portions of the article upon impact. In addition, the dry ice particles cool the im- [56] References cued pacted area and with thermoplastic and elastic materi- UNITED STATES TENTS als thereby embrittles thin sections of flashing and burrs and the like making them more easily removable gopphn i by the impact f the dry ice particles. trong 2,682,732 7/1954 l-lanrahan et a1. ..5 H13 X 15 Claims, 2 Drawing Figures 4 a o 46 o o .2 a 4 0 44 4 :4

PATENTEDrInmm 3.702.519

FIG. I

SPRAYING UNWANTED PORTIONS OF AN ARTICLE WITH HIGH VELOCITY SPRAY OF DRY ICE PART- STEP l ICLES UNTIL PORTIONS ARE REMOVED 1 METHOD FOR THE REMOVAL OF UNWANTED PORTIONS OF AN ARTICLE BY SPRAYING WITH VELOCITY DRY ICE PARTICLES PRIOR ART In general the prior art describes various methods of and equipment for the removal of unwanted portions of an article involving the use of conventional solid particles, such as finely divided sand, steel, glass and the like, which require subsequent removal, usually by washing, from internal portions of the treated article. In most'instances pre-cooling of the article is used to embrittle unwanted portions thereby facilitating their removal. Examples of such methods are those described in U.S. Pat. No. 2,996,846 Reissue No. Re. 25,554); 3,1 10,983; 3,137,101and 3,160,993.

In many instances pockets, holes and thelike in the article being treated accumulate or trap conventional solid particles making their removal difficult and expensive. This is particularly a problem where the articles being treated have blind or narrow internal passages or pockets.

Present methods using just high velocity particles are satisfactory for removing flashing and the like from thermoset plastics since such flashing is quite rigid and breaks upon impact with the particles. However, flashing and the like on thermoplastic and/or elastic materials tends to deform rather than to break and thus is not so easily removed.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method wherein the impacting material is easily removed from the treated article, particularly from internal passages inside an article being treated and can be removed without specific direct treatment by the user simply by allowing sublimation under ambient room temperature conditions. It is'further an 01 ject to provide a method wherein flashing, burrs and the like are easily removed from thermoplastic and/or elastic materials without the necessity of pre-cooling the article.

These and other objects will become increasingly apparent from the following description and the drawing.

FIG. 1 is a schematic diagram of the method of the present invention.

FIG. 2 schematically illustrates the preferred apparatus for spraying dry ice particles on the surface of an article to remove unwanted portions.

The objects of the present invention are accomplished by the method for the removal of unwanted portions of an article which comprises: impacting the unwanted portions with dry ice particles maintained under substantially anhydrous conditions so as to remove the unwanted portions. Any remaining dry ice particles are removed from the article using conditions favoring sublimation. As a result of merely storing, handling or processing the treated article at room temperature, the dry ice particles will sublimate so that there is no carbon dioxide residue remaining on the surface.

A related invention is disclosed in our copending application Ser. No. 122,152, filed Mar. 8, 1971, now U.S. Pat. No. 3,676,963, issued Feb. 8, 1972 wherein ice particles are used'with a cooling agent (such as liquid nitrogen or dry ice) as the abrasive medium. In the present invention the cooling agent is unnecessary since the dry ice particles themselves are at a tempera ture cooler than about --56C, (the triple point of carbon dioxide) and since the dry ice particles are flowable even when exposed to air at ambient temperatures. The present method using dry ice is particularly preferred where the material being treated might be adversely affected by water such as with the treatment of wood surfaces or electrical parts. Since dry ice sublimes at ambient conditions, dry ice removal after impacting the article is easily accomplished.

The particles are readily formed using conventional crushing techniques from largerblocks of dry ice and then screening the resulting dry ice particles for size. Alternatively the particles can be formed by freezing carbon dioxide in a cooling agent gas (hydrogen or helium) or liquid stream (liquid nitrogen), at a temperature lower than about 56C, although this is not preferred for cost reasons. In any event, the dry ice is maintained under substantially anhydrous conditions so that water and/or ice does not contaminate the article being impacted with the dry ice. Obviously small amounts of atmospheric moisture introducedinto the dry ice will have little affect on the method of the present invention.

Non-aqueous diluents can be used with the dry ice so long as they are not a solvent for, or a reactant with, the

article being treated and which can be removed under conditions favoring the removal of carbon dioxide. Examples of diluents which can satisfactorily be mixed with the dry ice particles and which evaporate under conditions favoring sublimation of the dry ice are liquids such as liquid nitrogen or lower alkanols'. Elevated or reduced pressures can be used to regulate the physical state of the diluent with the dry ice particles; however, ambient pressures are preferred for reasons of economy. Preferably the diluent is a vapor at ambient room temperatures and thus is removed by normal warming of the article after treatment.

' Various means can be used to impact the dry ice particles on the unwanted portions of an article. For instance, a gas stream can be driven through a conventional aspirator nozzle such that dry ice particles are aspirated into the gas stream through a conduit leading into the stream using a vacuum effect. The dry ice particles can be supplied directly to a gas stream which then exits through a nozzle. Gas blowers or airless mechanical impellers for the dry ice particles can be used. Air at 50-150 psig is particularly preferred to aspirate and then drive the dry ice particles for impacting. All of these expedients are well known to those skilled in the art. The selection is easily made depending upon the kinetic energy required to remove unwanted portions from a particular article with dry ice particles due to its construction or composition.

The dry ice particles additionally function to embrittle thin unwanted portions present as part of the impacted portions of the article. This embrittlement greatly aids in the removal of the thin portions upon subsequent impact by dry ice particles and is particularly useful with thermoplastic or elastomeric articles due to the rigidifying of thin sections whose flexibility makes their removal difficult at ambient temperatures. This result is particularly evident with flashing or burrs on flexible, elastic or thermoplastic polymers both natural and synthetic wherein such embrittlement aids the removal of the flashing, membranes or burrs. In addition, energy is conserved as only treated areas are Subjected to cooling. In this way delicate articles that might be damaged by complete cooling would have only the treated area differentially cooled.

Plastics, metals, ceramics and the like can be treated by the method of the present invention providing the dry ice particles are impacted against the unwanted portions of articles composed of such materials with sufficient energy. The treatment of the relatively softer or more flexible articles is particularly preferred since the action of the ice is most effective against unwanted portions of these articles.

Articles having all sorts of shapes due to fabricating steps can be treated by the method of the present invention and such fabrication includes machining, stamping, molding and the one two-hundredth dry ice spray is particularly useful for instance as an improved method for the reticulation (cell membrane removal) of sheets of foam materials such as cellular polyester or polyether polyurethanes and other polymer foams to make the cells more open and interconnected. In this instance, the easy self-removal of the impacting agent is particularly necessary and would be extremely difficult if conventional non-volatile particles were used because of the large number and small diameters of the cells and their consequent filtering and entrapment acnon.

The dry ice particles are easily and economically removed by sublimation. In some instances it may be desirable to .use a heated gas stream or a vacuum for forced sublimation or alternatively to allow the article to dry by warming to ambient conditions. Various methods for removing the dry ice particles are well known to those skilled in the art.

The dry ice particles can be of any desired size depending upon the application. For instance, it is preferred for reticulating foam that the particles have a diameter between about one-two hundredth inch and one-sixteenth inch. This allows the particles to easily penetrate the small internal passages of the above discussed foams. Thus where articles have internal passages requiring treatment, the particles should easily enter such passages. Conversely, if treatment is to be avoided, the particles should be larger than the passages or impact otherwise restricted such as by mask means with openings to softer sections of an underlying article. Also, large pellets or particles of dry ice can be used which shatter on impact with a surface.

SPECIFIC DESCRIPTION The following are non-limiting specific examples of the method of the present invention.

EXAMPLE I Referring to FIGS. 1 and 2 ice particles were reduced to a particle size passing through a 16 mesh screen. An aspirator nozzle 11 with about a 0.2 inch diameter dry ice pick-up conduit tube 12 and 0.3 inch diameter discharge opening 13 with a small orifice 14 (0.1 inch in diameter) concentric with the discharge opening 13 and just upstream of the conduit tube 12 was used with the dry ice particles 10. The section of nozzle 11 downstream from the dry ice inlet to the opening 13 was about 4 inches long. Air from a compressor l5 driven through the orifice l4 aspirated the dry ice particles 10 from a container 16 and then the air passing through the discharge opening 13 accelerated the particles 10 through the discharge opening 13. The air pressure upstream of the orifice 14 from the compressor 15 supply was about 150 pounds per square inch gauge.

A block of white pine 17 was then impacted with the dry ice particle spray. It was found that the soft portion 18 between the annular rings 19 was effectively removed to provide a weathered appearance. Preferably the dry ice particles 10 have a diameter less than the distance between the annular rings 19. A similar result was achieved with walnut, Douglas fir, ash and white oak. The effect was less pronounced with the harder woods such as ash and oak but clearly evident. Equivalent results were obtained in removing flashing from rubber 0 rings, rust (including red and blue oxides) from steel parts and deburring metals and plastics, such as methyl methacrylate.

EXAMPLE II The surface of a sheet of polyester polyurethane foam (about 10 pores per linear inch, about 2.0 pounds per cubic foot and one-quarter inch thick) was sprayed in the manner of Example I using air at 60 psig and 16 mesh screened dry ice to remove the membranes from the cells. The sheet was completely reticulated and the remaining cell struts were firm and intact. In all instances, the entrapped or residual dry ice was easily removed by sublimation upon warming to ambient temperatures.

EXAMPLE III The procedure of Example 11 was repeated with another polyester polyurethane foam sheet with a much smaller pore size pores per lineal inch; 2.0 pounds per cubic foot density and one-eighth inch thick). The dry ice passed 16 mesh screening. The

sheet was completely reticulated without damage to the skeletal structure.

EXAMPLE IV The procedure of Example I was repeated with a thin aluminum sheet having depressions about every oneeighth inch to remove a surface aluminum oxide which was tenaceously adhered to the surface. The dry ice was 10 mesh. The dry ice spray was produced with air at psig. It was found that the oxides were removed and the aluminum sheet was not visibly damaged by the treatment.

EXAMPLE V The procedure of Example I was repeated using 10 mesh screened dry ice impacted on a rosin-fluxed soldered joint between a copper tube /8 inch OD.) and woven wire using air at to psig. It was found that the joint was completely cleaned of the rosin flux. Also the copper tubing around the soldered joint was cleaned by removal of surface oxides. No damage was done to the joint or the tube.

EXAMPLE v1 Ethanol as a diluent was added to crushed dry ice passing through a 16 mesh screen in a ratio of l to l by volume to form a slush." The mixture was sprayed in the apparatus of Example I and the burrs on a polyethylene rod were removed. Various plastic parts were also deburred, the only limitation being that the ethanol does not significantly dissolve the plastic. Rust was also removed from steel parts with this mixture. This dry ice-ethanol mixture was also pressurized directly out of a nozzle rather than aspirated. This was accomplished by using high pressure bottled nitrogen to pressurize the mixture to about 800 psi and it satisfactorily deflashed the treated articles such as a nylon part with a mold flash. Drying was accomplished by warming to ambient temperatures to remove the ethanol.

EXAMPLE VII A second aspirator nozzle similar to that of Example I was used with a l inch diameter discharge nozzle and a 0.15 inch orifice about 1 inch upstream from a k inch inlet opening for the dry ice at a right angle to the nozzle. The nozzle was 8 inches long past the dry ice inlet opening. Dry ice particles no larger than three-sixteenths inch in diameter were aspirated from the container, with boiling liquid nitrogen (about minus 295F) driven through the orifice and nozzle. Mold flash on hot formed glass filled polyropylene sheet was completely removed without damage to the remainder of the article.

It will be appreciated that various airless techniques can also be utilized as are known in the prior art wherein the ice particles derive momentum by means other than from a gas stream as for example by centrifugal force.

EXAMPLE Vlll To illustrate the airless technique a blower with radially extending vanes 4 inches long and 1% inches wide rotating on a shaft in a housing was used. An inlet reservoir funnel attached to the blower housing for dry ice pellets (large particles) about one-half inch in diameter fed the pellets to the rotating vanes, which shattered them into smaller dry ice particles and exited them through a tangential outlet. Cast aluminum which had been milled leaving burrs was effectively deburred.

The following example shows the use of a mixture of ice and a lower alkanol as the cooling agent.

EXAMPLE 1x A mixture of equal parts by volume of dry ice particles and methyl alcohol as a diluent in equal parts by volume was prepared as a slush. The mixture was loaded into a cylindrical gun about 20 inches long and with a 2% inch diameter. A 3/16 inch diameter bore discharge nozzle was located at one end of the gun. A filler plug was provided at the breech of the gun and the gun was connected through the filler plug to a high pressure nitrogen tank (1,500 psi). The gun was charged with the dry ice particles-methanol mixture and the nitrogen source triggered so thatthe gun discharged about perpendicularly to a projection of flashing on a zinc diecast part. It was found that the flashing was completely removed from the part by the methyl alcohol dry ice particle mixture. The mixture was easily removed under ambient conditions.

The dry ice can be mixed with small amounts of various chemical agents such as preservatives. Thus chemicals which produce a grey weathered appearance can be introduced into the dry ice. This and other obvious variations will occur to those skilled in the art.

We claim:

1. The method for producing raised annular rings on the surface of wood which comprises:

spraying the surface with a high velocity spray of dry ice particles maintained under substantially anhydrous conditions until the softer portions between the annular rings are abraded away.

2. The method of claim 1 wherein the wood is a softwood.

3. The method of claim 1 wherein the softwood is pine. 4. The method of claim 1 wherein the dry ice particles are mixed with a chemical agent fortreating the surface of the wood which is driven into the wood upon impact.

5. The method of claim 4 wherein the chemical agent produces a grey weathered appearance.

6. The method of claim 1 wherein the step of spraying of the dry ice particles is accomplished by their being carried in an elevated pressure gas stream directed towards the wood surface for impact.

7. The method of claim 1 wherein the step of spraying of the dry ice particles is accomplished by their being mechanically driven towards the wood surface for impact.

8, The method of claim 1 wherein the step of spraying is accomplished by driving a gas stream such that it aspirates the dry ice particles into the gas stream directed towards the wood surface for impact.

9. The method of claim 1 wherein as an additional step the dry ice particles before spraying are subjected to screening so that the particles have a diameter of less than the distance between the annular rings.

10. The method of claim 1 wherein as an additional step before spraying a larger block of solid carbon dioxide is subjected to crushing to produce the dry ice particles.

11. The method of removing relatively softer sections disposed between harder sections on a surface which comprises:

spraying the surface with a high velocity spray of particles of dry ice maintained under substantially anhydrous conditions until at least a portion of the relatively softer sections between the harder sections are abraded away.

12. The method of claim 11 including the additional step before spraying of covering the harder sections on the surface with masking means with openings to softer sections of an underlying surface.

13. The method for the removal of unwanted portions of an article which are relatively more susceptible to removal with sprayed high velocity particles which comprises:

spraying the article including the unwanted portions with a high velocity spray of dry ice particles maintained under substantially anhydrous conditions until the unwanted portions are removed.

14. The method of claim 13 wherein the step of spraying of the dry ice particles is accomplished by aspiration of the particles into an air stream at an upstream pressure between about 50 and 150 psig directed towards the article for impact.

15. The method of claim 13 wherein the unwanted portions of the article which are removed are thin membranes dividing contiguous cells in a foam. 

1. The method for producing raised annular rings on the surface of wood which comprises: spraying the surface with a high velocity spray of dry ice particles maintained under substantially anhydrous conditions until the softer portions between the annular rings are abraded away.
 2. The method of claim 1 wherein the wood is a softwood.
 3. The method of claim 1 wherein the softwood is pine.
 4. The method of claim 1 wherein the dry ice particles are mixed with a chemical agent for treating the surface of the wood which is driven into the wood upon impact.
 5. The method of claim 4 wherein the chemical agent produces a grey weathered appearance.
 6. The method of claim 1 wherein the step of spraying of the dry ice particles is accomplished by their being carried in an elevated pressure gas stream directed towards the wood surface for impact.
 7. The method of claim 1 wherein the step of spraying of the dry ice particles is accomplished by their being mechanically driven towards the wood surface for impact. 8, The method of claim 1 wherein the step of spraying is accomplished by driving a gas stream such that it aspirates the dry ice particles into the gas stream directed towards the wood surface for impact.
 9. The method of claim 1 wherein as an additional step the dry ice particles before spraying are subjected to screening so that the particles have a diameter of less than the distance between the annular rings.
 10. The method of claim 1 wherein as an additional step before spraying a larger block of solid carbon dioxide is subjected to crushing to produce the dry ice particles.
 11. The method of removing relatively softer sections disposed between harder sections on a surface which comprises: spraying the surface with a high velocity spray of particles of dry ice maintained under substantially anhydrous conditions until at least a portion of the relatively softer sections between the harder sections are abraded away.
 12. The method of claim 11 including the additional step before spraying of covering the harder sections on the surface with masking means with openings to softer sections of an underlying surface.
 13. The method for the removal of unwanted portions of an article which are relatively more susceptible to removal with sprayed high vElocity particles which comprises: spraying the article including the unwanted portions with a high velocity spray of dry ice particles maintained under substantially anhydrous conditions until the unwanted portions are removed.
 14. The method of claim 13 wherein the step of spraying of the dry ice particles is accomplished by aspiration of the particles into an air stream at an upstream pressure between about 50 and 150 psig directed towards the article for impact.
 15. The method of claim 13 wherein the unwanted portions of the article which are removed are thin membranes dividing contiguous cells in a foam. 